The continuous technology scaling has made the design of amplifiers in nanoscale CMOS very challenging. Nanoscale CMOS technologies are characterized not only by smaller transistor sizes but also by shrinking supply voltages. Thus, conventional amplifier design techniques, where amplifiers are designed by representing signal information in the voltage and current domains, suffer from a number of disadvantages in scaled technologies. For example, the shrinking power supply voltage leads to limited voltage headroom, and hence a large power consumption is required to achieve a certain signal-to-noise ratio (SNR) because of signal swing limitations. The shrinking power supply voltage also leads to poor linearity. In addition, the intrinsic gain of transistors degrades in scaled CMOS technologies.
Recently, techniques have been proposed to design amplifiers that largely address the limitations of conventional design techniques in the following references: B. Drost et. al, “Analog Filter Design Using Ring Oscillator Integrators,” IEEE Journal of Solid-State Circuits, vol. 47, no. 12, December 2012 (hereinafter “Drost”); B. Vigraham et. al, “Switched-Mode Operational Amplifiers and Their Application to Continuous-Time Filters in Nanoscale CMOS,” IEEE Journal of Solid-State Circuits, vol. 49, no. 12, December 2014 (hereinafter “Vigraham I”); and B. Vigraham et. al, “Circuits and Methods for Switched-Mode Operational Amplifiers,” US Patent No. 2016/0226451A1 (hereinafter “Vigraham II”). By exploiting the faster devices available in scaled CMOS technologies, Drost, Vigraham I, and Vigraham II propose amplifiers that represent signal information in the time domain, rather than the voltage and current domains as used by conventional design techniques. But, the designs proposed in Drost suffers from poor linearity, resulting from its inherent “open-loop” structure. The design proposed in Vigraham I and Vigraham II, while addressing the linearity concerns in Drost, suffer from increased complexity leading to larger circuit area and power consumption.
We propose Ring-Oscillator operational amplifiers to address voltage headroom challenges for analog design in scaled CMOS technologies, as well addressing the limitations of Dorst, Vigraham I, and Vigraham II.